I think we are all familiar with the illusion of the moon looking much larger than its true angular size when it is near the horizon, but there's a less familiar moon-related illusion that I only really noticed for myself when I was out running a few years ago. It turns out to be well-documented, and well-understood, but no less weird, because even when you "know" the explanation, your brain still won't readily accept it - or at least, mine won't.

Anyway, today was an ideal day to observe the mo...